A) The presence of air makes it impossible to connect a vacuum pump, which is necessary to perform the evacuation procedure.
B) Too much air makes it impossible to properly calibrate an analog vacuum gauge within the refrigeration system.
C) Oxygen may violently react with hydrogen and potentially cause a fire within the refrigeration system.
D) Oxygen will chemically react with the refrigeration oil and deposits buildup in the discharge valve area, causing compressor motor burnouts.